This invention relates to the conversion of coal and similar carbonaceous solids into liquids and is particularly concerned with a coal conversion process carried out in the absence of an externally added hydrocarbon solvent.
Processes for the conversion of coal and similar carbonaceous solids into hydrocarbon liquids normally require contacting of the solid feed material with a hydrocarbon solvent and molecular hydrogen at elevated temperature and pressure to break down the complex high molecular weight starting material into lower molecular weight hydrocarbon liquids and gases. The most promising processes of this type are those carried out with a hydrogen-donor solvent which gives up hydrogen atoms for reaction with organic radicals liberated from the coal or other feed material during the conversion or liquefaction step. In such a process, a portion of the liquids produced in the liquefaction reactor is recovered and catalytically hydrogenated in a solvent hydrogenation reactor to generate the hydrogen-donor solvent required in the liquefaction step. The heavy liquefaction product, which normally boils in excess of about 1000.degree. F., recovered from the liquefaction reactor may be upgraded by subjecting it to pyrolysis to produce gases, additional hydrocarbon liquids, and coke which is subsequently steam gasified to form hydrogen and carbon monoxide for use as fuel.
Although hydrogen-donor liquefaction has numerous advantages over other liquefaction processes and produces a relatively large amount of liquids, it does require the use of a donor solvent produced by hydrogenating a portion of the liquid product in an external catalytic hydrogenation reactor. The production of this hydrogen-donor recycle solvent stream via catalytic hydrogenation external to the liquefaction step adds appreciably to the cost of the process and it would therefore be economically attractive if the recycle stream could be eliminated without decreasing the liquid yield from the process.